Aircraft seating is typically divided into various classes, for example first class, business class, and coach class. For each class of seating, an individual passenger is allotted a preselected amount of space (both area and volume). First-class seats provide the most individual space, and also may include features to improve comfort, such as fully reclining sleeper functions. In contrast, the coach class, and sometimes the business class is provided with a relatively small amount of space, in order to provide the most efficient transportation and lowest cost.
Typically, passengers are more satisfied by a given quantity of space when that space is completely controlled by the passenger. Since the space for coach-class seating is limited, it is especially important that a passenger's personal space be protected from intrusion from other passengers. However, coach class seats are generally arranged such that passengers that are seated side-by side must share a single armrest. In this arrangement, the armrest width allotted to each passenger, and the dividing line between adjacent seats, is not clearly delineated. Often people will encroach into what is intended to be the space of the person seated next to them. This can lead to conflicts between passengers as each tries to assert control of the single armrest, as well as discomfort of the passenger that gets a smaller portion of the armrest or no armrest at all.